Curable inkjet printable ink compositions

ABSTRACT

The invention provides curable ink compositions that are inkjet printable and that adhere to a variety of substrates, for example, glass and polymer. The ink compositions of the invention can be formulated so to provide cured inks that are very flexible or very rigid depending upon the desired application. The invention provides a cure-on-demand curable ink composition including a homogeneous mixture of at least one of: (a) a compound having 2 reactive silyl groups, and (b) a compound having at least 3 reactive silyl groups; acid generating catalyst; and pigment or pigment chip. The invention also provides methods of making and using the ink compositions and imaged articles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/430,913, filed on Nov. 1, 1999, now U.S. Pat. No. 6,461,419, thedisclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to moisture curable ink compositions,particularly to those having reactive silyl functionality and their use.

BACKGROUND OF THE INVENTION

Moisture-curable compositions cure in the presence of moisture to formcrosslinked materials. The moisture is typically obtained from theatmosphere or from a substrate to which the composition has beenapplied, although it may be added to the composition.

Most moisture-curable compositions are based on isocyanate containingcompounds. However, these compositions have well known disadvantages.Other moisture-curable compositions comprise polymers having groups (forexample, alkoxysilyl or acyloxysilyl moieties) that react in thepresence of moisture to form cured (i.e., crosslinked) materials.Moisture-curable compositions comprising alkoxysilyl or acyloxysilylfunctionality typically cure in two reactions. In the first reaction,the alkoxysilyl or acyloxysilyl groups hydrolyze in the presence ofmoisture and a catalyst to form compounds having silanol groups. In thesecond reaction, the silanol groups condense with other silanol,alkoxysilyl, or acyloxysilyl groups in the presence of a catalyst toform —Si—O—Si— linkages. The two reactions occur essentiallysimultaneously upon generation of the silanol-functional compound.Commonly used catalysts for the two reactions include Brönsted and Lewisacids. A single material may catalyze both reactions.

The hydrolysis reaction is schematically illustrated below for a polymerhaving alkoxysilyl groups:

The resulting silanol (SiOH) groups are not stable in the presence ofthe acid catalyst and immediately condense with other silanol oralkoxysilyl group to form —Si—O—Si— linkages as shown belowschematically for the condensation reaction of a silanol-functionalcompound and an alkoxysilyl-functional compound:

Preferably, the hydrolysis and condensation reactions proceed quicklyonce the moisture-curable composition has been applied, for example, toa substrate.

Such compositions have been described as being useful as adhesives,sealants, and coatings.

Some known silane ink compositions contain an acid or a base added ascatalysts in the ink binder. Such inks tend to have short pot-lives. Theshelf life of such ink compositions is dependent upon the concentrationof hydrolyzible silane compounds so the inks typically contain largeamounts of solvents or water. Attempts to increase the shelf life ofsuch inks include first hydrolyzing and condensing the alkoxysilylcompounds under controlled conditions and then use the reaction productas part of the ink binder.

Other curable siloxane ink compositions do not contain a catalyst, insome instances, to increase that storage stability of the ink. Theseinks require that they be heated to 150-200° C. for 5-10 minutes toaccelerate the hydrolysis reaction or that they are reacted very slowlyat controlled temperature and humidity. Inks that require heating arenot suitable for use on substrates that have a relatively low meltingpoint or are easily distorted with heat. And, such slow curing willaffect the printing resolution, due to uncontrolled spread of the drops,and color bleeding.

Most curable inks are based on acrylate and epoxy chemistries. Theacrylate based inks cure rapidly by free-radical reaction and have goodweatherability. However, the acrylate-based inks also typically sufferfrom oxygen inhibition during cure and surface shrinkage that cancontribute to low gloss.

Epoxy-based inks have less shrinkage than acrylate-based inks, providegood adhesion, and have no oxygen inhibition during cure. However,epoxy-based inks typically provide poor weatherability and may haverelatively slow cationic reaction rates as compared to free radicalreaction rates.

SUMMARY OF THE INVENTION

The invention provides curable ink compositions that are inkjetprintable and that adhere to a variety of substrates, for example, glassand polymer. “Curable” means that either reactive silyl groups hydrolyzein the presence of moisture to form compounds having silanol groups thatreact in the presence of an activated catalyst to form —Si—O—Si—linkages or silanol groups react in the presence of an activatedcatalyst to form —Si—O—Si— linkages.

The ink compositions of the invention can be formulated so as to providecured inks that are very flexible, that is, polydimethylsiloxane, orvery rigid, that is, silicate, depending upon the desired application.The curable ink compositions are also shelf stable and arecured-on-demand in that they may be cured rapidly at a predeterminedtime. “Shelf stable” means that the compositions are stable in a lightprotected container for at least 3 weeks and preferably for at least 6months. The ink compositions of the invention also provide inks havinghigh gloss and transparency. The ink compositions of the invention alsoare not required to be diluted with water or solvent in order to bestable.

In one aspect, the invention provides a cure-on-demand curable inkcomposition comprising a homogeneous mixture of at least one of: (a) acompound having 2 reactive silyl groups, and (b) a compound having atleast 3 reactive silyl groups; acid generating catalyst; and pigment orpigment chip. The acid generating catalyst may be activated (liberate aBrönsted or Lewis acid) by heat or irradiating the composition with, forexample, ultraviolet, visible light, electron beam, or microwaveradiation.

In another aspect, the invention provides inks that are ink-jetprintable.

In another aspect, the invention provides imaged ceramic articlescomprising a cured ink composition of the invention on a ceramicsubstrate.

In another aspect, the invention provides a method of making acure-on-demand curable ink composition comprising the steps of:

sequentially combining a compound having at least 3 reactive silylgroups, pigment chip, and acid generating catalyst with constant mixing.

In another aspect, the invention provides a method of forming an imagedarticle comprising the step of inkjet printing a moisture curable inkcomposition of the invention onto a substrate.

In another aspect, the invention provides a cure-on-demand curablecomposition for overprinting images comprising a homogeneous mixture ofat least one of: (a) a compound having 2 reactive silyl groups, and (b)a compound having at least 3 reactive silyl groups; and acid generatingcatalyst.

The curable ink compositions of the invention can be formulated to haveexcellent adhesion to a variety of substrates, for example, those ofpolymethylmethacrylate (PMMA), silicone rubber, ceramics, and glass. Theink compositions of the invention also cure rapidly at room temperatureand are expected to have excellent outdoor weatherability due to theirinorganic backbone.

DETAILED DESCRIPTION OF THE INVENTION

Reactive Silyl Functional Compounds

The curable ink compositions of the invention contain at least one of 1)a compound having at least two reactive silyl groups per molecule,typically a silicon atom bonded to either two hydroxysilyl groups or twoalkoxysilyl groups and 2) a compound having at least 3 reactive silylgroups per molecule. The ink compositions of the invention also maycontain a mixture of compounds from both of the above classes ofcompounds.

Reactive silyl functional compounds useful in the invention canincorporate a wide variety of backbones to support the reactive silylgroups and, as a result, such compounds may be generally represented bythe following structures:

wherein,

A is a k-valent group which may be selected from, for example, achemical bond (i.e., no atoms); —OR; alkyl groups (preferably having 1to 30, more preferably, 12 to 20 carbon atoms); cycloalkyl groups(preferably having 3 to 30, more preferably, 6 to 10 carbon atoms), arylgroups (preferably having from 6 to about 30 carbon atoms); a chalcogen(group VIb elements), such as oxygen, sulfur, etc., and polymericradicals which may be of linear, branched, block, or graft construction.Non-limiting examples of suitable polymeric groups includepolysiloxanes, polyacrylates, polyamides, polyolefins, polyethers,polyesters, polyurethanes and polyphosphazenes, as well as derivativesand combinations thereof. The polymeric groups may be hydroxy-(to form asilanol), acyloxy-, or alkoxy-terminated or may have pendent silanol,acyloxysilyl, or alkoxysilyl groups.

Each G independently represents an optional multi-valent group having avalence of at least 2. Non-limiting examples of G include —Si(OR)_(x)—wherein x=0-2, hydrocarbon diyls and oxydiyls, particularly alkanediylsand oxydiyls, such as methylidene, ethylidene, 1,3-propanediyl,1,5-pentanediyl, 2-oxo-propanediyl, phenylene (an arenediyl);chalcogens, such as oxygen, sulfur, etc.; hydrocarbon triyls, such as,for example, pentaerythritoltriyl; and the like. The exact nature of Gis not critical so long as it does not contain groups that inhibit thecondensation cure of alkoxy- or hydroxysilyl groups.

Each R₁ independently represents hydrogen, an alkyl group (preferablyhaving 1 to 30, more preferably, 1 to 4 carbon atoms), a cycloalkylgroup (preferably having 3 to 30, more preferably, 6 to 10 carbonatoms), an alkanoyl group (preferably having 2 to 30, more preferably, 2to 4 carbon atoms), or an aroyl group (preferably having from 7 to about30 carbon atoms).

Each R independently represents hydrogen, an alkyl group (preferablyhaving 1 to 30, more preferably, 1 to 10 carbon atoms), a cycloalkylgroup (preferably having 3 to 30, more preferably, 6 to 10 carbonatoms), an alkanoyl group (preferably having 2 to 30, more preferably, 2to 10 carbon atoms), or an aroyl group (preferably having from 7 toabout 30 carbon atoms).

Each n is either 0, 1, or 2 with the proviso that compounds from eitherStructure 1 or Structure 2 above have at least two reactive silylgroups; each j independently represents 0 or an integer greater than orequal to 1; k represents an integer greater than or equal to 1; and mrepresents an integer greater than or equal to 3.

As is well understood in this area, substitution is not only tolerated,but also is often advisable and substitution is anticipated on thecompounds used in the present invention. As a means of simplifying thediscussion and recitation of certain substituent groups, the terms“group” and “moiety” are used to differentiate between those chemicalspecies that may be substituted and those which may not be sosubstituted. Thus, when the term “group” or “aryl group” is used todescribe a substituent, that substituent includes the use of additionalsubstituents beyond the literal definition of the basic group. Where theterm “moiety” is used to describe a substituent, only the unsubstitutedgroup is intended to be included. For example, the phrase, “alkyl group”is intended to include not only pure hydrocarbon alkyl chains, such asmethyl, ethyl, propyl, t-butyl, cyclohexyl, iso-octyl, octadecyl and thelike, but also alkyl chains bearing substituents known in the art, suchas hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano,nitro, carboxy, etc. For example, alkyl group includes ether groups(e.g., CH₂CH₂CH₂—O—), haloalkyls, nitroalkyls, carboxyalkyls,hydroxyalkyls, sulfoalkyls, etc.

On the other hand, the phrase “alkyl moiety” is limited to the inclusionof only pure hydrocarbon alkyl chains, such as methyl, ethyl, propyl,t-butyl, iso-octyl, octadecyl, and the like. Substituents that reactwith active ingredients, such as very strongly electrophilic oroxidizing substituents, or basic materials that would substantiallyinterfere with the cationic curing catalyst (e.g., tertiary amines,etc.) would of course be excluded by the ordinarily skilled artisan asnot being inert or harmless.

As noted above, preferred groups for radical A include silanol- oralkoxy-terminated polysiloxanes, polyacrylates, polyolefins andpolyether

1. Difunctional Silane Compounds

The compositions of the invention can contain at least one difunctionalsilane compound, for example, having either two silanol groups or twoalkoxysilyl groups per molecule. These compounds provide a polymerbackbone and adjust crosslink density of the cured inks.

Nonlimiting, specific examples of compounds described above includehydroxy and/or alkoxy terminated polydimethylsiloxanes having amolecular weight of 400 to 150,000; hydroxy and/or alkoxy terminateddiphenylsiloxane-dimethylsiloxane copolymers; hydroxy and/or alkoxyterminated polydiphenylsiloxanes; hydroxysilyl and/or alkoxysilylterminated polytrifluoropropylmethylsiloxanes, polyesters,polyurethanes, and polyacrylates; dialkyl- and substituted dialkyl-dialkoxysilanes, such as diethyldiethoxysilane, dimethyldimethoxysilane,diethyldiethoxysilane, diisobutyldimethoxysilane,dimethyldiethoxysilane, diisopropyldimethoxysilane,bis(3-cyanopropyl)dimethoxysilane, (2-chloroethyl)methyldimethoxysilane,chloromethylmethyldiethoxysilane,(2-chloroethyl)methyldiisopropoxysilane,(3-chloropropyl)methyldimethoxysilane,(3-cyanopropyl)methyldimethoxysilane,cyclohexylethyldimethoxysilane, dodecylmethyldiethoxysilane,isobutylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane;mercaptomethylmethyldiethsysilane,methacryloxypropylmethyldiethoxysilane,methacryloxypropylmethyldimethoxysilane, methyldiethoxysilane,methyldimethoxysilane, n-octadecylmethyldiethoxysilane;n-octylmethyldiethoxysilane, dicyclopentyldimethoxysilane, etc.; aryland diaryl substituted alkoxysilanes, such as diphenyldimethoxysilane,phenyldiethoxysilane, phenylmethyldiethoxysilane,phenylmethyldimethoxysilane, etc.; hydroxysilyl and alkoxysilylsubstituted arenes, such as 1,4-bis(hydroxydimethylsilyl)benzene,1,3-bis(methoxydimethylsilyl)benzene, etc.; trialkylsilyl substitutedalkoxysilanes, such as bis(trimethylsilylmethyl)dimethoxysilane,trimethylsilylmethyldimethoxysilane,etc.; cyclic alkoxysilanes, such as1,1-diethoxy-1-silacyclopent-3-ene, etc.; acyloxy substituted silanes,such as dimethyldiacetoxysilane, vinylmethyldiacetoxysilane,diethylbenzoyloxyacetoxysilane, etc; geminal silanediols, such asdiphenylsilanediol, dicyclohexylsilanediol, etc.; alkyl and/or arylsubstituted cyclic siloxanes, such as3-(3,3,3-trifluoropropyl)heptamethyltrisiloxane, hexamethyltrisiloxane,octamethyltetrasiloxane, etc.; alkenyl substituted alkoxysilanes, suchas vinylmethyldiethoxysilane, vinylmethyldimethoxysilane,vinylphenyldiethoxysilane, and the like.

Presently preferred compounds having 2 reactive silyl groups are hydroxyterminated polydimethylsiloxanes and polydiethylsiloxanes (i.e., havingSi—OH terminal groups).

2. Silanes Having at Least 3 Reactive Silyl Groups

The compositions of the invention can contain at least one compoundhaving at least 3 and preferably, from 4 to 6 reactive silyl groups permolecule. The reactive silyl groups can be, for example, alkoxy silyl oracyloxy silyl groups.

Nonlimiting, specific examples of compounds described above includetrifunctional crosslinkers, such as, for example,isobutyltrimethoxysilane, methytriethoxysilane, methytrimethoxysilane,octyltriethoxysilane, propyltrimethoxysilane, phenyltrimethoxysilane,chloropropyltriethoxysilane, chloroproyltrimethoxysilane,mercaptopropyltrimethoxysilane, glycidyloxypropyltrimethoxysilane,methacryloxypropyltrimethoxysilane, vinyltriethoxysilane,vinyltrimethoxysilane; tetrafunctional crosslinkers, such as, forexample, tetramethoxysilane, tetraethoxysilane,1,3-dimethyltetramethoxydisiloxane,1,3-di-n-octyltetramethoxydisiloxane, 1,3-divinyltetraethoxydisiloxane,1,1,3,3-tetraethoxy-1,3-dimethyldisiloxane,tetrakis(butoxyethoxyethoxy)silane, tetrakis(ethoxyethoxy)silane,tetrakis(trimethylsiloxy)silane, tetrakis(2-ethylhexoxy)silane,tetrakis(2-methacryloxyethoxysilane),tetrakis(methoxyethoxyethoxy)silane, tetrakis(methoxyethoxy)silane,tetrakis(methoxypropoxy)silane, tetra-n-propoxysilane; higherfunctionality crosslinkers, such asbis[3-(methyldimethoxysilyl)propyl]-polypropylene oxide,bis(triethoxysilyl)ethane, bis(triethoxysilyl)ethylene,bio(triethoxysilyl)methane, 1,9-bis(triethoxysilyl)nonane,bis(triethoxysilyl)1,7-octadiene, bis(triethoxysilyl)octane,bis[3-(triethoxysilyl)propyl]-tetrasulfide,bis(3-(triethoxysilyl)propyl)urea, bis(trimethoxysilyl)ethane,1,4-bis(trimethoxysilylethyl)benzene, bis(trimethoxysilyl)hexane,bis(trimethylsiloxy)cyclobutene, di-t-butoxydiacetoxysilane,hexamethoxydisilane, hexaethoxydisilane, tetraacetoxysilane,tetraallyloxysilane, tetra-n-butoxysilane,1-(triethoxysilyl)-2-(diethoxymethylsilyl)ethane, and functionalpolymers, such as poly(diethoxysiloxane),diethoxysiloxane-s-butylaluminate copolymers,diethoxysiloxane-ethyltitanate copolymers, diethoxysiloxane-ethylphosphate copolymers, and the like.

Presently preferred compounds having 3 or more reactive silane groupsare 1,3-dimethyltetramethoxydisiloxane,methacryloxypropyltrimethoxysilane, tetraethoxysilane,1,3-dioctyltetramethoxydisiloxane, glycidoxypropyltrimethoxysilane,3-bromopropyltrimethoxysilane, and dioctyltetraethoxydisiloxane.

Preferably, the reactive silyl functional groups are the only acidcurable groups in the ink composition.

Acid Generating Catalysts

Upon activation, the acid generating catalyst liberates an acid thatinitiates and/or accelerates curing (i.e., crosslinking) of the curableink composition. In order to facilitate more rapid curing, the liberatedacid preferably has a pKa of less than about 3, more preferably lessthan about 1. Activation may be accomplished by heat or irradiating thecomposition with, for example, ultraviolet, visible light, electron beamor microwave radiation. Moisture required for the initial hydrolysisreaction of the curing mechanism may be obtained from, for example, thesubstrate, the composition itself, or, most commonly, atmospherichumidity. The catalyst is typically present in an amount of about 0.5 toabout 20 parts by weight, preferably from about I to about 10 parts byweight, more preferably from about 2 to about 7 parts by weight based on100 parts by weight reactive silane functional compounds.

A variety of catalysts may be used in the practice of the inventionexcept for those containing basic species, such as ammonium saltsdisclosed in U.S. Pat. No. 5,286,815 that generate an amine that mayinhibit the curing reaction of the cure-on-demand composition of thisinvention. Thus, catalysts of the present invention are substantiallyfree of ammonium salts. Minor amounts of such salts may be toleratedwithout greatly affecting the care rate. Particularly desired catalystsfor use in this invention are those that are capable of releasing anacid upon exposure to ultraviolet or visible light or upon exposure toelectron beam irradiation. Preferably, the catalyst comprises an oniumsalt because of their capacity to simultaneously generate a strong acidand an energetic free radical when activated.

Onium salts suitable for use in the present invention are preferablysulfonium or iodonium salts having the following structure:

L_(W)—Y⁺MX⁻  Structure 3

L is an aryl or substituted aryl group; w is an integer from 2 to 4; Yis sulfur or iodine; M is a Group III, IV, or V element from thePeriodic Table of the Elements; and X is a sulfate, tosylate,alkylsulfonate, fluoroalkylsulfonate, fluoroalkyl, or a perfluorinatedaryl group.

Examples of useful sulfonium salts include:

triphenylsulfonium tetrafluoroborate;

triphenylsulfonium tetrakis(pentafluorobenzyl)borate;

methyldiphenylsulfonium tetrafluoroborate;

methyldiphenylsulfonium tetrakis(pentafluorobenzyl)borate;

dimethylphenylsulfonium hexafluorophosphate;

triphenylsulfonium hexafluorophosphate;

triphenylsulfonium hexafluoroantimonate;

diphenylnaphthylsulfonium hexafluoroarsenate;

tritolysulfonium hexafluorophosphate;

anisyldiphenylsulfonium hexafluorantimonate;

4-butoxyphenyldiphenylsulfonium tetrafluoroborate;

4-butoxyphenyldiphenylsulfonium tetrakis(pentafluorobenzyl)borate;

4-chlorophenyldiphenylsulfonium hexafluoroantimonate;

tris(4-phenoxyphenyl)sulfonium hexafluorophosphate;

di(4-ethoxyphenyl)methylsulfonium hexafluoroarsenate;

4-acetylphenyldiphenylsulfonium tetrafluoroborate;

4-acetylphenyldiphenylsulfonium tetrakis(pentafluorobenzyl)borate;

tris(4-thiomethoxyphenyl)sulfonium hexafluorophosphate;

di(methoxysulfonylphenyl)methylsulfonium hexafluoroantimonate;

di(methoxynaphthyl)methylsulfonium tetrafluoroborate;

di(methoxynaphthyl)methylsulfonium tetrakis(pentafluorobenzyl)borate;

di(carbomethoxyphenyl)methylsulfonium hexafluorophosphate;

(4-octyloxyphenyl)diphenylsulfoniumtetrakis(3,5-bis-trifluoromethylphenyl)borate;

tris(dodecylphenyl)sulfoniumtetrakis(3,5-bis-trifluoromethylphenyl)borate;

4-acetamidophenyldiphenylsulfonium tetrafluoroborate;

4-acetamidophenyldiphenylsulfonium tetrakis(pentafluorobenzyl)borate;

dimethylnaphthylsulfonium hexafluorophosphate;

trifluoromethyldiphenylsulfonium tetrafluoroborate;

trifluoromethyldiphenylsulfonium tetrakis(pentafluorobenzyl)borate;

phenylmethylbenzylsulfonium hexafluorophosphate;

10-methylphenoxathiinium hexafluorophosphate;

5-methylthianthrenium hexafluorophosphate;

10-phenyl-9,9-dimethylthioxanthenium hexafluorophosphate;

10-phenyl-9-oxothioxanthenium tetrafluoroborate;

10-phenyl-9-oxothioxanthenium tetrakis(pentafluorobenzyl)borate;

5-methyl-10-oxothianthrenium tetrafluoroborate;

5-methyl-10-oxothianthrenium tetrakis(pentafluorobenzyl)borate; and

5-methyl-10,10-dioxothianthrenium hexafluorophosphate.

Examples of useful iodonium salts include: di(dodecylphenyl)iodoniumhexafluoroantimonate, di(dodecylphenyl)iodonium triflate;diphenyliodonium bisulfate, 4,4′-dichlorodiphenyliodonium bisulfate;4,4′-dibromodiphenyliodonium bisulfate; 3,3′-dinitrodiphenyliodoniumbisulf 4,4′-dimethyldiphenyliodonium bisulfate;4,4′-bissuccinimidodiphenyliodonium bisulfate; 3-nitrodiphenyliodoniumbisulfate; 4,4′-dimethoxydiphenyliodonium bisulfate,bis(dodecylphenyl)iodonium tetrakis(pentafluorophenyl)borate;(4-octyloxyphenyl)phenyliodonium tetrakis(3,5-bis-trifluoromethylphenyl)borate; (tolylcumyl)iodonium tetrakis(pentafluorophenyl)borate(CH₃C₆H₄)₂I—(SO₂CF₃)₃, as disclosed in U.S. Pat. No. 5,554,664;(C₆H₅)₂I—B(C₆F₅)₄, as disclosed in U.S. Pat. No. 5,514,728; and thosedisclosed in U.S. Pat. No. 5,340,898. A particularly preferred oniumsalt is di(dodecylphenyl)iodonium hexafluoroantimonate.

Onium salts are typically activated using ultraviolet radiation. Becauseof this, they can be advantageously employed in applications involvingheat-sensitive substrates. Optionally, a sensitizer may supplement theonium salt to accelerate the liberation of the acid catalyst and typicalamounts are about 0.03 to about 0.1 parts by weight, based on 100 partsby weight reactive silane functional compound. Examples of suitablesensitizers include those described in Chapter 13 of Radiation Curing inPolymer Science and Technology, Vol. 2, edited by Fouassier and Rabek,Elsevier Science Publishers LTD, 1993. 2-isopropylthioxanthone is aparticularly preferred sensitizer for use with di(dodecylphenyl)iodoniumhexafluoroantimonate.

Pigments

The ink compositions of the invention contain one or more pigments.Suitable organic and inorganic pigments include carbon black, zincoxide, titanium dioxide, phthalocyanine, anthraquinones, perylenes,carbazoles, monoazo- and disazobenzimidazolones, rhodamines, indigoids,quinacridones, diazopyranthrones, dinitranilines, pyrazolones,diazopyranthrones, dinitranilines, pyrazolones, dianisidines,pyranthrones, tetracholoroisoindolinones, dioxazines, monoazoacrylides,and anthrapyrimidines. It will be recognized by those skilled in the artthat organic pigments will be differently shaded, or even have differentcolors, depending on the functional groups attached to the mainmolecule.

Commercial examples of useful organic pigments include those known underthe C.I. (i.e., Colour Index International, 3rd ed., 4th revision(1992-); The Society of Dyers and Colourists, Bradford, West Yorkshire,England) trade designations PB1, PB15, PB15:1, PB15:2, PB15:3, PB15:4,PB15:5, PB15:6, PB16, and PB60 (blue pigment); PB5, PB23, and PB265(brown pigment); PG1, PG7, PG10, PG36 (green pigment); PY3, PY14, PY16,PY17, PY24, PY65, PY73, PY83, PY95, PY97, PY108, PY109, PY110, PY113,PY128, PY129, PY138, PY139, PY150, PY154, PY156, and PY175 (yellowpigment); PO5, PO15, PO16, P031, P034, PO36, P043, P048, PO51, PO60 andPO61 (orange pigments); PR4, PR5, PR7, PR9, PR222, PR23, PR48, PR48:2,PR49, PR1 12, PR123, PR149, PR166, PR168, PR170, PR177, PR179, PR190,PR202, PR206, PR207, PR224 (red); PV19, PV23, PV37, PV32 and PV42(violet pigments); and PBLACK (black).

The pigments are milled so to incorporate into selected curable inkvehicles. If used as inkjet inks, the pigment preferably is less than 1micrometer in size after milling. If the ink to be used in applicationwherein the ink is used in combination with a retroreflective backing,the pigment must be milled to a particle size that provide sufficienttransparency to permit retroreflection and provide retroreflectivecolor. The preferred range for the pigment particle size is about 10-400nm, more preferably 10 to 200 nm, to provide the desired transparency.

In some cases, pigment is ground with a non-reactive binder resin whichseparates pigment particles and prevents them from coalescing. Suchsolid/solid dispersion, referred to as pigment chip, maintains pigmentparticle size until the pigment is ready to be incorporated into theink. The ratio of pigment to binder resin in the supplied chip isusually about 1:1 to 9:1. Useful binder resins for use in the inks ofthe current invention are well known in the pigment dispersion art andinclude cellulosic resins, such as ethyl cellulose, cellulose acetate,nitrocellulose, etc.; acrylic resins, such as those sold under the tradedesignation JONCRYL from S. C. Johnson Wax, Racine, Wis.; polyacetalresins, such as polyvinyl butral (for example, those sold under thetrade designation BUTVAR from Monsanto Co., St. Louis, Mo.) andpolyvinyl formal (for example, those sold under the trade designationFORMVAR from Monsanto Co.); and modified rosin ester resins and thelike.

The preferred pigment chip in the ink of the current invention containspigments, such as titanium dioxide or carbon black and ethyl celluloseresin. Such pigment chips are available under the trade name MICROLITHWhite R-A and MICROLITH Black C-A from Ciba Specialty ChemicalsDivision, Newport, Del.

An effective amount of pigment is used to provide the desired color andintensity to the ink. The vehicle maybe be used, for example, in anamount ranging from about 20-99.9 percent of the weight of the totalcomposition and a colorant from about 0.1 to 80 percent of the totalcomposition.

Solvents

A solvent may be included in the ink compositions of the invention todecrease the viscosity of the composition. Solvent should be misciblewith the other components of the ink compositions of the invention.Examples of useful solvents include ketones and alcohols. Suitableketones include acetone, cyclohexanone, and methyl ethyl ketone.Suitable alcohols include methanol and ethanol. Other solvents that maybe useful include acetonitrile, carbon tetrachloride, dichloroethane,dicloromethane, dimethylformamide, dimethylsulfoxide, ethyl acetate,diethyl ether, diisopropyl ether, tetrachloroethane, tetrahydrofuran,and trichloroethane. If present, solvent may be from 0.1 to 30 percent,preferably, 0.1 to 10 percent by weight of the ink composition, morepreferably, less than 10 percent and even more preferably, solvent free.

Optional Additives

Conventional additives, such as flow agents, leveling agents, viscositymodifiers, antioxidants, hindered amine light stabilizers, UV lightabsorbers, electrolytes (to provide electrical conductivity), and thelike, may be added to the compositions of the invention. If used, theseadditives may be individually present in an amount ranging from about0.5 to 5 weight percent of the ink composition.

Ink Compositions

Preparation of stable curable ink compositions of the invention isreadily accomplished through the following procedures. Preparation ofstable inks of the invention is not readily achieved by simply mixingpigment into the ink vehicle.

However, it has been found that if pigment chip is being used, adispersibility test is run to determine the ability of the at leasttrifunctional silane to disperse the pigment chip. The dispersibilitytest is as follows: 0.1 g of the pigment chip to be dispersed in the inkand having the desired particle size is added to a clear glass vialcontaining 1.0 g of at least trifunctional silane. The ink in thecontainer is vigorously stirred with a stirring rod for 1 minute andthen allowed to stand for about 10 minutes. If no settling of thepigment is observed when viewing through the vial, then the test ispassed and is considered to be dispersible.

In the event that the pigment chip dispersibility test is passed, thenthe ink composition may be prepared by sequentially combining, in acontainer equipped with mixing means, at least trifunctional silane,pigment chip, difunctional silane, curative, and any optional solvent(to be used reduce viscosity).

In the event that the pigment chip dispersibility test is failed, thenthe ink composition may be prepared in a container equipped with mixingmeans, by sequentially combining (in order) pigment chip, sufficientsolvent to create a homogeneous solution, at least a trifunctionalsilane, difunctional silane, curative, and any optional solvent.

In the event that regular pigment is used to make the curable inkcompositions of the invention, then the ink composition may be preparedby sequentially combining, in a container equipped with mixing means, asilicone surfactant, pigment, any optional at least trifunctionalsilane, difunctional silane and processing for sufficient time so as toform a dispersion concentrate. Then curative and any optional solvent isadded with mixing.

Useful silicone surfactants include polyalkylene oxide modifiedpolydimethylsiloxane (mw=100-15,000 g/mol, preferably, 300-5000 g/mol).Examples include SILWET L77, L7608, L7280, L7607, L722, L7500, L7602,L7622, L7604, L7057, L7605, L7600, and L7002 and are available fromWitco Corp., Greenwich, Conn.

In the event that a phthalocyanine pigment is used to make the curableink compositions of the invention, then the ink composition mayoptionally also be prepared by sequentially combining, in a containerequipped with mixing means, pigment, any optional at least trifunctionalsilane, difunctional silane, and processing for sufficient time so as toform a dispersion concentrate. Curative, and any optional solvent isadded with mixing. “Mixing means” includes shearing mixers, two or threeroll mills, media mills, ball mills, agitators, and the like.

The physical properties and adhesion characteristics of the inks of theinvention may be tailored for specific end uses. The characteristics ofthe cured inks largely depend upon the ratio of difunctional silanes andat least trifunctional silanes. For example, inks that are generallypliable and have good adhesion to low surface energy substrates usuallycontain more difunctional silane than at least trifunctional silane. Onthe other hand, inks that are generally rigid and which have goodadhesion to surface, such as glass and ceramic usually contain more atleast trifunctional silane than difunctional silane.

The ink compositions which are generally pliable after cure contain fromabout 10 to about 90 weight percent compound having 2 reactive silylgroups, from about 5 to about 40 weight percent compound having at least3 reactive silyl groups, from about 0.1 to about 20 percent by weightacid generating catalyst, and from about 0.1 to about 80 percent byweight pigment. The preferred ranges are about 30 to about 50 weightpercent compound having 2 reactive silyl groups, from about 15 to about25 weight percent of compound having at least 3 reactive silyl groups,from about 0.5 to about 5 weight percent acid generating catalyst, andfrom about 2 to about 15 weight percent pigment.

The ink compositions which are generally rigid after cure and have goodadhesion to glass and ceramic contain from 0 to about 10 weight percentof compound having 2 reactive silyl groups, from about 40 to about 95weight percent of compound having at least 3 reactive silyl groups, fromabout 0.1 to about 20 weight percent acid generating catalyst, and fromabout 0.2 to about 80 weight percent pigment. The preferred ranges arefrom about 2 to about 5 weight percent of compound having 2 reactivesilyl groups, from about 50 to about 80 weight percent of compoundhaving at least three reactive silyl groups, from about 0.5 to about 5weight percent of acid generating catalyst, and from about 2 to about 15weight percent pigment.

The ink compositions of the invention can have a Brookfield viscosity ofup to about 50 cps (mPa s) preferably about 25 cps (mPa s), morepreferably less than about 15 cps (mPa s) at 25° C.

The ink compositions of the invention may be applied to a substrateusing conventional ink printing techniques, such as screen printing,flexographic, and offset, etc. However, the ink compositions of theinvention are particularly well adapted for ink-jet printing techniques.Once printed, the ink compositions will react with the moisture in theambient air and/or the catalyst will be activated by UV light and formcured ink. The cured ink may be rigid or pliable depending upon thespecific formula of ingredients used.

In some instances, it may be desirable to further heat the substrate andthe ink until the ink is converted into a ceramic material free ofcarbonaceous matter, that is, to pyrolyze the printed substrate.

Once a substrate has been imaged with ink of the invention, it may bedesirable to coat the image with a pigment-free or clear coatcomposition to enhance weatherability and durability of the image. Suchclear coat compositions can be made by combining acid generatingcatalyst with at least one of: (a) a compound having 2 reactive silylgroups, and (b) a compound having at least 3 reactive silyl groups. Thecharacteristics of the clear coat compositions can be tailored asdescribed above for the ink compositions. The clear coat compositionsmay be applied over the image using any means and is preferably appliedover the image and/or substrate using inkjet printing techniques.

EXAMPLES

MICROLITH pigment chip was obtained from Ciba Specialty Chemicals,Pigments Division of Newport, Del.; MICROLITH A WHITE R-A is a 75 weightpercent dispersion of C.I. Pigment White 6 (titanium dioxide) in anethyl cellulose carrier resin; yellow pigment chip MICROLITH T 3R-T is a40 weight percent dispersion of C.I. Pigment Yellow 110 in a modifiedrosin ester; MICROLITH A BLACK C-A is a 60 weight percent dispersion ofC.I. Pigment Black 7 in an ethyl cellulose carrier resin.

RAVEN 1200 FURNACE BLACK (C.I. Pigment Black 7) was obtained fromColumbian Chemical Co. Inc. of Marietta, Ga.

Ceramic media (0.3 mm) were obtained from SEPR Co. of Saint-GobainIndustrial Ceramics Inc. of Mountainside, N.J.

Viscosity measurements were made using a BROOKFIELD CAP 2000 cone-plateviscometer available from Brookfield Engineering Laboratories, Inc. ofMiddleboro, Mass. at a temperature of 25° C.

The printer testbed had a Modular Ink Technology of Stockholm, Sweden(MIT) printhead (30 pL drop-volume, 128 nozzle) and a motor driventable. The table moves in the Y direction and the printhead moves in theX direction and utilizes software to control the patterns. The heightbetween the printhead to the table is about 1.5-2 mm and is availablefrom MIT (a division of Nu-kote)

MICROFAB printhead, refers to a squeeze mood single nozzle piezoelectricinkjet printhead obtained from MicroFab Technologies, Inc. of Plano,Tex. The diameter of the printhead nozzle is 50 micrometer. Thefrequency of the jetting is 1 kHz. Pressure (P), voltages (V₁ and V₂)and pulse time (T ₁ and T₂) were adjusted in order to achieve theoptimal jetting condition. Inks were filtered with 1 micrometer glassfilter before loading in the ink reservoir.

3M COLD SHRINK QSIII, is a silicone rubber medium voltage Cold Shrinksplice used in distribution of electric power obtained from 3M Companyof Austin, Tex.

HP 500s refers to the black ink used in 51626A HP Black Inkjet PrintCartridges, available from Hewlett-Packard Company, Inc. of Palo Alto,Calif.

Nu-kote inkjet inks were pigment dispersions in high boiling hydrocarbonsolvents and were obtained from Nu-kote International, Inc. of Franklin,Tenn.

The “silicone release liner” used in the following examples was asilicone coated polyester film.

Teflon seal tape was obtained from E. I. du Pont de Nemours and Co. ofWilmington, Del.

Mayer rods were obtained from R&D Specialties of Whittier, Calif.

TCM Diamond Grade (DG) refers to 3M™ Scotchlite™ Diamond Grade™ VIP(visual impact performance) Reflective Sheeting #3970 is available from3M Company of St. Paul, Minn.

High Intensity Sheeting (HIS) refers to 3M™ Scotchlite™ High IntensityGrade Reflective Sheeting Series #3870, available from 3M Company.

“INTRATHERM YELLOW 346” is a yellow dye obtained from Crompton & KnowlesCorp. of Stamford, Conn.

PIGMENT BLUE 15:1 was obtained from BASF Corp. of Budd Lake, N.J.

“RHODORSIL PHOTOINITIATOR 2074” (trade designation for[(1-methylethyl)phenyl](methylphenyl)iodoniumtetrakis(pentafluorophenyl)borate) is available from Rhodia, Inc. ofCranbury, N.J.

3M Transparent Film Tape 610 is sold by 3M Company of St. Paul, Minn.

“MEK” means methyl ethyl ketone.

Methacryloxypropyltrimethoxysilane, tetraethoxysilane,1,3-dimethyltetramethoxy-disiloxane and3-glycidoxypropyltrimethoxysilane were obtained from United ChemicalsTechnologies, Inc., Petrarch Systems of Bristol, Pa.

Silanol terminated polydimethylsiloxane was obtained from Gelest Inc. ofTullytown, Pa.

Triethoxysilane terminated polydimethylsiloxane was obtained from GelestInc.

SILWET L77 is a silicone dispersant (polyethylene oxide-silicone blockcopolymer, AP type (alkyl pendant chain), MW 600, PEO around 70 percent)obtained from Witco, Inc. of Greenwich, Conn.

Polydiethoxysiloxane was obtained from Gelest, Inc.

All inks prepared in the following examples were passed through a 1micrometer diameter pore size glass filter unless otherwise noted.

Unless otherwise specified materials used in the following examples wereobtained from general chemical supply sources, such as, for example,Aldrich Chemical Co. of Milwaukee, Wis.

EXAMPLE 1

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant. “Silicone based” ink means an inkthat is generally pliable after cure.

To 10 parts MICROLITH A WHITE R-A was added 10 parts cyclohexanone, 20parts 1,3-dimethyltetramethoxydisiloxane, 20 partsmethacryloxypropyltrimethoxysilane and 40 parts silanol terminatedpolydimethylsiloxane (20-35 cps (mPa s)). The ink was ground in a ballmill using 0.3 mm diameter ceramic media for 2 hours and 3 parts ofRHODORSIL PHOTOINITIATOR 2074 was added with mixing. The ink wasfiltered with 1 micrometer diameter pore size glass filter.

The ink solution was coated onto black 3M COLD SHRINK QSIII siliconerubber with a #6 Mayer rod (wet film thickness 0.14 cm). The coating wascured with a Fusion UV Systems processor using an “H”-type bulb.Exposure conditions were 200 mJ/cm² at 50 ft/min.

After curing, the ink binder was essentially a crosslinked polysiloxane.The ink was formulated with viscosity of 10-12 centipoise (cps (mPa s)),and successfully jetted with a piezoelectric inkjet printer testbed asdescribed above with good consistency. The ink coating showed 100percent adhesion (as measured by 90 degree tape snap on a cross-hatchedfilm according to ASTM D3359-95a, Test Method B), and good colorcontrast on the black 3M COLD SHRINK QSIII substrate. The coatingremained unchanged after immersing the coated samples in 5M NaCl for 90days and at 60° C. for 7 days. The ink coating was rubbery and veryflexible and did not break when folded to 180 degrees. The inkformulation was stable after 3 month storage at room temperature.

EXAMPLE 2

This example demonstrates utility of the ink prepared in Example 1. Theadvancing contact angle for various ink formulations are listed in Table1 (measured according to ASTM D5946 using a Rame-Hart contact anglegoniometer: A drop of liquid ink was placed on the surface of thesubstrate and the advancing contact angle values were measured 3 timesand averaged). In each case, the silicone ink of Example 1 had superiorwet out to conventional inks.

TABLE 1 Advancing Contact Angle Measurements Of Inks On DifferentSubstrates Water- Oil-based ink Silicone based ink (from Nu-kote inkfrom (HP 500s) International) Example 1 3M Cold Shrink ™ QSIII 90 44 26Silicone release liner, 88 28 21 (obtained from 3M Company of St. Paul,MN, core series: 19-9850) TEFLON seal tape 86 26 20

EXAMPLE 3

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant. “Silicate based” refers to ink thatis generally rigid after cure.

To 6 parts MICROLITH A WHITE R-A was added 75 parts tetraethoxysilane(available from Fluka Chemical Corp., Milwaukee, Wis.) and 25 partsmethacryloxypropyltrimethoxysilane. The solution was ground in a ballmill using 0.3 mm diameter ceramic media for 2 hours. Three parts ofRHODORSIL PHOTOINIATOR 2074 was added with mixing and the solution wasfiltered. The viscosity of the ink was 13-15 cps (mPa s). The ink wascoated on polymethyl methacrylate (PMMA) sheeting with a #6 Mayer rod(nominal wet film thickness was 0.14 cm). Exposure conditions were 190mJ/cm² at 50 ft/min. The cured coating was hard and glossy.

The coating showed 100 percent adhesion on 3M Diamond Grade (DG) and 3MHigh Intensity Sheeting (HIS). The adhesion was measured by 90 degreetape snap on a cross-hatched film according to ASTM D3359-95a, TestMethod B. 100 percent adhesion corresponding to no removal of thesquares, 0 percent corresponding with removal of all squares.

Durability of the ink coating was tested. There was no change ofadhesion, judging from 90 degree cross-hatch snap test using 3M tape#610 (ASTM D3359-95a, Test Method B), when the coating was immersedwater for 90 days, or in acid solution (0.1 M HCl) for 90 days, or at55° C. at 100 percent humidity for 2 days. In addition, the coatingshowed excellent solvent resistance (60-80 MEK double Rubs: A hammerhead was fitted with a piece of felt secured by a rubber band. Thedevice was soaked in the solvent of interest and rubbed by hand acrossthe coating using a gentle back and forth motion (one cycle is a doublerub). The number of double rubs was recorded when the coating in therubbed area had been completely removed.) and abrasion resistance basedon steel wool test consisting of lightly rubbing the surface of the inkcoating with steel wool 3 double rubs.

EXAMPLE 4

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts of MICROLITH A WHITE R-A was added 10 parts cyclohexanoneand mixed well to form a uniform paste. Gradually, 80 parts1,3-dimethyltetramethoxydisiloxane was added to the paste with mixing.the solution was ground in a ball mill using 2 mm diameter glass beadsfor 2 hours. Three parts RHODORSIL PHOTOINIATOR 2074 was added withmixing and the solution was filtered. The ink was stable for at least 1day. It cured very fast under conditions described in Example 1, showing10-20 percent adhesion to QSIII as described therein.

EXAMPLE 5

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 20 parts of MICROLITH A WHITE R-A was added 20 parts 1-propanol andmixed well to form a uniform paste. Gradually, 60 parts1,3-dioctyltetraethoxydisiloxane was added to the paste with mixing.Three parts RHODORSIL PHOTOINIATOR 2047 was added and the solution wasground in a ball mill using 2 mm diameter glass beads for 2 hours andfiltered. The ink was stable for at least 1 day, and cured to giveresults as in Example 4.

EXAMPLE 6

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts of MICROLITH A WHITE R-A was added 10 parts cyclohexanoneand 40 parts tetraethoxysilane and mixed well to form a uniform paste.Gradually, 40 parts silanol terminated polydimethylsiloxane (20-35 cps(mPa s)) was added to the paste with mixing. The solution was ground ina ball mill using 2 mm diameter glass beads for 2 hours. Three partsRHODORSIL PHOTOINIATOR 2074 was added with mixing and the solution wasfiltered. The ink was stable up to 1 day. The ink cured very fastaccording the conditions of Example 1, and exhibited 20-30 percentadhesion to QSIII as described therein.

EXAMPLE 7

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts of MICROLITH A WHITE R-A was added 10 parts cyclohexanone,20 parts methacryloxypropyltrimethoxysilane and 20 parts1,3-dioctyltetraethoxydisiloxane and mixed well to form a uniform paste.Gradually, 40 parts silanol terminated polydimethylsiloxane (20-35 cps(mPa s)) was added to the paste with mixing. The ink was ground in aball mill using 2 mm diameter glass beads for 2 hours. Three partsRHODORSIL PHOTOINIATOR were added with mixing and the ink was filtered.The ink which had a viscosity of 31 cps (mPa s) was stable for at least3 days. The ink cured rapidly under the conditions described in Example1 and had 100 percent adhesion to QSIII as described therein.

EXAMPLE 8

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts of MICROLITH A WHITE R-A was added 10 parts cyclohexanone,20 parts methacryloxypropyltrimethoxysilane and 20 parts1,3-dioctyltetraethoxydisiloxane and mixed well to form a uniform paste.Gradually, 80 parts silanol terminated polydimethylsiloxane (20-35 cps(mPa s)) was added to the paste with mixing. The ink was ground in aball mill using 0.3 mm diameter ceramic media for 2 hours and 3 partsRHODORSIL PHOTOINIATOR were added with mixing. The ink was filtered with1 micrometer diameter pore size glass filter. The ink which had aviscosity of 33 cps (mPa s) was stable for at least 3 days. The inkcured rapidly under the conditions described in Example 1 and had 100percent adhesion to 3M COLD SHRINK QSIII substrate as described therein.

EXAMPLE 9

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts of MICROLITH A WHITE R-A was added 10 parts cyclohexanone,20 parts methacryloxypropyltrimethoxysilane and 20 partstetraethoxysilane and mixed well to form a uniform paste. Gradually, 40parts silanol terminated polydimethylsiloxane (20-35 cps (mPa s)) wasadded to the paste with mixing. The ink was ground in a ball mill using0.3 mm diameter ceramic media for 2 hours and 3 parts RHODORSILPHOTOINIATOR were added with mixing. The ink was filtered with 1micrometer diameter pore size glass filter. The ink was stable for atleast 7 days. The ink cured rapidly under the conditions described inExample 1 and had good wetting and 70 percent adhesion to siliconerelease liner as described in Example 2.

EXAMPLE 10

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 7 parts MICROLITH A WHITE R-A were added 10 parts cyclohexanone, 20parts 1,3-dimethyltetramethoxydisiloxane, 20 partsmethacryloxypropyltrimethoxysilane and 40 parts silanol terminatedpolydimethylsiloxane (20-35 cps (mPa s)). The ink was ground in a ballmill using 0.3 mm diameter ceramic media for 2 hours and 3 partsRHODORSIL PHOTOINITIATOR 2074 were added with mixing. The ink wasfiltered with 1 micrometer diameter pore size glass filter. The ink,which had a viscosity of 13 cps (mPa s), was stable for at least 7 days.It cured quickly under conditions as described in Example 1, and had 100percent adhesion to QSIII as described therein. The ink was successfullyinkjet printed as described in Example 1.

EXAMPLE 11

This example describes the preparation of a silicone based ink whereinpigment chip was used as colorant.

To 10 parts MICROLITH A BLACK C-A pigment chip was added 10 partscyclohexanone, 20 parts 1,3-dimethyltetramethoxydisiloxane, 20 partsmethacryloxypropyltrimethoxysilane and 40 parts s (mPa s)). The ink wasground in a ball mill using 0.3 mm diameter ceramic media for 2 hoursand 3 parts of RHODORSIL PHOTOINIATOR 2074 was added with mixing. Theink was filtered with 1 micrometer diameter pore size glass filter. Theink was stable for at least 7 days. After curing under conditions asdescribed in Example 1, it gave a glossy ink with 80 percent adhesion to3M High Intensity Sheeting as described therein. Some dewets wereobserved in the coating.

EXAMPLE 12

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 10 parts Microlith A Black C-A pigment chip was added 10 partscyclohexanone, 20 parts tetraethoxysilane, 20 partsmethacryloxypropyltrimethoxysilane and 40 parts silanol terminatedpolydimethylsiloxane (20-35 cps (mPa s)). The ink was ground in a ballmill using 0.3 mm diameter ceramic media for 2 hours and 3 partsRHODORSI PHOTOINIATOR were added with mixing. The ink was filtered with1 micrometer diameter pore size glass filter. The ink was stable for atleast 7 days. After curing under conditions as described in Example 1,it gave a glossy ink with 0 percent adhesion to 3M High IntensitySheeting as described therein. No dewets were observed in the coating.

EXAMPLE 13

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 10 parts Microlith A Black C-A pigment chip was added 10 partscyclohexanone, 40 parts tetraethoxysilane, 20 partsmethacryloxypropyltrimethoxysilane and 20 parts silanol terminatedpolydimethylsiloxane (20-35 cps (mPa s)). The ink was ground in a ballmill using 0.3 mm diameter ceramic media for 2 hours and 3 parts ofRHODORSIL PHOTOINIATOR 2074 was added with mixing. The ink was filteredwith 1 micrometer diameter pore size glass filter. The ink was stablefor at least 7 days. After curing under conditions as described inExample 1, it gave a glossy ink with 0 to 30 percent adhesion to 3M HighIntensity Sheeting as described therein. No dewets were observed in thecoating.

EXAMPLE 14

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 10 parts MICROLITH A BLACK C-A pigment chip was added 10 partscyclohexanone, 40 parts tetraethoxysilane and 40 parts silanolterminated polydimethylsiloxane (20-35 cps (mPa s)). The ink was groundin a ball mill using 0.3 mm diameter ceramic media for 2 hours and 3parts of RHODORSIL PHOTOINIATOR 2074 was added with mixing. The ink wasfiltered with 1 micrometer diameter pore size glass filter. The ink wasstable for at least 7 days. After curing under conditions as describedin Example 1, 60 to 80 percent adhesion to 3M High Intensity Sheetingwas observed as described therein. No dewets were observed in thecoating.

EXAMPLE 15

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 10 parts MICROLITH A BLACK C-A pigment chip was added 10 partscyclohexanone, 60 parts tetraethoxysilane and 20 partsmethacryloxypropyltrimethoxysilane. The ink was ground in a ball millusing 0.3 mm diameter ceramic media for 2 hours and 3 parts of RHODORSILPHOTOINIATOR 2074 was added with mixing. The ink was filtered with 1micrometer diameter pore size glass filter. The ink was stable for atleast 7 days. After curing under conditions as described in Example 1,it gave a glossy ink with 60 to 80 percent adhesion to both 3M HighIntensity and 3M Diamond Grade Sheeting was observed as describedtherein. No dewets were observed in the coating.

EXAMPLE 16

This example describes the preparation of a silicate based ink whereinpigment chip was used as colorant.

To 10 parts MICROLITH A BLACK C-A pigment chip was added 67.5 partstetraethoxysilane and 22.5 parts methacryloxypropyltrimethoxysilane. Theink was ground in a ball mill using 0.3 mm diameter ceramic media for 2hours and 3 parts of RHODORSIL PHOTOINIATOR 2074 was added with mixing.The ink was filtered with 1 micrometer diameter pore size glass filter.The ink was stable for at least 14 days. After curing under conditionsas described in Example 1, it gave a glossy ink with 100 percentadhesion to both 3M High Intensity and 3M Diamond Grade Sheeting wasobserved as described therein. No dewets were observed in the coating.

EXAMPLE 17

This example the utility of inks according to the present invention.Unless otherwise specified inks were coated and cured as described inExample 1.

Ink Method of Composition Substrate application Ink Adhesion Siliconeink Silicone rubber #6 Mayer rod 100% from QSIII Microfab printhead 100%Example 10 Testbed printer  80%* (MIT printhead) Silicone release Meyercoat  70% liner Testbed printer  50% (MIT printhead) Fluoropolymer THV#6 Mayer rod 5-10% Testbed printer  10% (MIT printhead) S-BOPP #6 Mayerrod 100% PET #6 Mayer rod 100% Silicate ink Retroreflective #6 Mayer rod100% from sheeting (HIS) Example 16 Retroreflective Testbed printer  50%(except 7.5% sheeting (HIS) (MIT printhead) pigment RetroreflectiveMeyer bar coat 100% chips) sheeting (DG) Testbed printer 50-70%*  (MITprinthead) Paper Testbed printer Not Tested (MIT printhead) Silicate inkGlass #6 Mayer rod 100% from Example 16 *Adhesion of jetted film wasgenerally less than Mayer rod coated, the reason might have to do withthe curing lamp available on the printer which was not in the preferredwavelength range for initiator used in formulation. The curing conditionwas a light intensity of about 11 w/cm².

EXAMPLE 18

This example demonstrates the jetting of a silicone-based ink. An inkwas prepared as follows.

To 5 parts Microlith R-A, were added sequentially with mixing 10 partscyclohexanone, 20 parts 1,3-dimethyltetramethoxydisiloxane and 20 partsmethacryloxypropyltrimethoxysilane are added. The mixture was mixed wellto form a uniform paste, followed by addition of 40 parts silanolterminated polydimethylsiloxane gradually. The ink was ground in a ballmill using 0.3-mm diameter ceramic media for 2 hours. The ink wasfiltered with 1 micrometer diameter pore size glass filter. To the inkwas added 5 parts RHODORSIL PHOTOINIATOR 2074. The resultant ink had ameasured viscosity of 12.6 cps (mPa s).

As a control, a solution containing no Microlith R-A was also preparedby mixing solutions in the above formulation. The measured viscosity ofthis solution was 4.7 cps (mPa s).

Jettability of the ink was tested using Microfab printhead, which is asqueeze mood single nozzle piezoelectric inkjet printhead. The diameterof the printhead nozzle is 50 micrometer. The frequency of the jettingis 1 kHz. Pressure (P), voltages (V₁ and V₂) and pulse time (T₁ and T₂)were adjusted in order to achieve the optimal jetting condition. Inkswere filtered with 1 micrometer glass filter before loaded in the inkreservoir.

The above ink was jetted consistently at pressure −4.21 to −4.37 units,V₁=0 to −5, V₂=−100 to −95, T₁=100 μs, T₂=80 to 100 μs. The siliconesolution with no pigment chip was jetted at pressure −4.49, V₁=−5 to−25, V₂=−95 to −75, T₁=50 −80 μs, T₂=55-80 μs. In both cases, the largerthe V₁ and T₁ the jetted droplets have less satellites formation yetlonger tails. Both the ink and solution was jetted on QSIII siliconerubber. Surprisingly the solution didn't seem to flow significantly uponreaching the substrates.

EXAMPLE 19

The example demonstrates inkjet printing of silicone based inksaccording to the present invention onto a silicone rubber substrate.

A solution was prepared using 10 parts cyclohexanone, 20 parts1,3-dimethyltetramethoxydisiloxane, 40 parts of silanol terminatedpolydimethylsiloxane and 20 parts methacryloxypropyltrimethoxysilane.The solution was mixed well with a magnetic stir bar for 30 minutes.

A pigment millbase was prepared by vigorously mixing 10 parts MICROLITHR-A and 40 parts of the above solution using a blade mixer for 10-15minutes until homogeneous. Two inks with different pigment content wereprepared by diluting 2.0 parts and 2.7 parts of the millbase with 6parts of the above solution respectively and ball milling for 60minutes. To each of these inks was added 5 weight percent RHODORSILPHOTOINIATOR 2074. The measured ink viscosities of these inks was 10-13cps (mPa s). The inks were filtered through a 1 micrometer glass filter.

The inks were incorporated into a drop-on-demand inkjet printer testbed.Printed images were generated on silicone rubber QSIII. A medium mercurylamp was incorporated on the printer and radiation-cured the image whileit was printed. The images were produced either by 28 of the 56 nozzlesor by 52 of the 56 nozzles constantly firing. In both conditions the inkwas jetted and printed on the substrate with no detectable missing lines(nozzle clogging) during the entire printing process. The resultingimagings were white lines with sharp edge definitions and reasonablygood adhesion. The image with higher pigment content showed significantbetter color contrast to the black substrates.

EXAMPLE 20

The example demonstrates inkjet printing of a silicone based ink onto asilicone release liner

Ink was prepared as in Example 19. Images were produced by inkjetprinting the inks onto a silicone coated release liner. The testbed wasused with 52 out of 56 nozzles constantly firing. There were nodetectable missing lines during printing, indicating no nozzle clogging.The resulting imaging was white lines that wet the silicone liner verywell. The image exhibited good edge definition and good color contrast.

EXAMPLE 21

This example demonstrates inkjet printing of a silicate ink ontoretroreflective sheeting.

A solution was prepared by mixing 60 parts tetraethoxysilane and 20parts methacryloxypropyltrimethoxysilane. The solution was mixed wellwith magnetic stir bar for 30 minutes.

Three parts MICROLITH C-K was added to 27 parts of the above solutionand ground in a ball mill for 1-2 hours. To the mixture, 5 parts of thesolution and 5 parts cyclohexanone were added and mixed with magneticstir bar for 30 minutes. Next, 2 parts RHODORSIL PHOTOINIATOR 2074 wereadded and mixed for another 30 minutes. The measured viscosity of theink was 12.8 cps (mPa s) at 1000 rpm. The ink was filtered with 1micrometer glass filter.

The above ink was incorporated in drop-on-demand inkjet printer testbed.Images were printed on retroreflective sheeting High Intensity andDiamond Grade respectively. The printed ink was spot-cured using amedium mercury lamp (ULTRACURE 100SS PLUS obtained from ZFOS USA, Inc.)with an intensity of 11 W/cm² that followed the moving printhead andcured the image while printed. Both images were printed by constantfiring of 52 out of 56 nozzles of the printhead. The resulting imageswere straight black lines that exhibit excellent gloss and colorcontrast. The image showed reasonable adhesion on the substrates.

EXAMPLE 22

This example describes the preparation of a silicone based ink whereinpigment was used as colorant.

Polydiethoxysiloxane (6 parts, 8 cps (mPa s)), 2 partsmethacryloxytrimethoxysilane and 0.64 parts of SILWET L77 were combinedand well mixed. Gradually, 0.8 parts of COLUMBIA RAVEN 1200 FURNACEBLACK was added to solution with constant stirring. The mixture wasmilled in a ball mill with 12 parts 0.3 mm ceramic media at 10-20 rpmfor at least 18 hours. The resulting ink was stable for at least 12hours. RHODORSIL PHOTOINIATOR 2074 (0.24 parts) was added to the inksolution. The ink was coated on High Intensity Sheeting with a #6 Mayerbar (nominal wet thickness was 0.014 mm) and cured with a UV ProcessorModel MC-6ROH from Fusion U.V., Rockville, Md., using an H-type lamp atan intensity of 200 mJ/cm² and a total exposure of 128 W/cm². Thecoating showed 100 percent adhesion to HIS based on crosshatch 90 degreetape snap test (as in Example 3).

EXAMPLE 23

This example describes the preparation of a hybrid silicone/silicatebased ink wherein readily dispersible pigment was used as colorant.

PIGMENT BLUE 15:1 (0.5 parts) were mixed with 1.0 part silanolterminated polydimethysiloxane (20-30 cps (mPa s)), 6 partspolydiethoxysiloxane (8 cps (mPa s)) and 2 partsmethacryloxytrimethoxysilane. The mixture was milled in a ball millusing 15 parts of 0.33 mm ceramic media at 12 rpm for 18 hours. The inkwas stable for at least 12 hours. The viscosity of the resultant ink was7.3 cps (mPa s). To the ink solution was added 0.03 parts RHODORSILPHOTOINIATOR 2074. The ink was coated on High Intensity Sheeting with a#6 Mayer bar (nominal wet thickness was 0.014 mm) and cured as describedin Example 22 with a total exposure of 384 W/cm²). The coating showed100 percent crosshatch adhesion measured by ASTM D3359-95a, test MethodB.

EXAMPLE 24

This example describes the preparation of a hybrid silicone/silicatebased ink wherein readily dispersible pigment chip was used as colorant.

An ink vehicle solution was prepared by mixing 3 parts tetraethoxysilanewith 1 part methacryloxytrimethoxysilane.

A millbase was prepared by combining 10 parts MICROLITH C-K pigment chipwith 40 parts of the ink vehicle solution. The mixture was mixed with ablade mixer until homogeneous. The millbase contained 20 percent pigmentchip.

Millbase (2 parts) was mixed with 6 parts the of ink vehicle solution.To the solution was added 0.24 parts silanol terminatedpolydimethysiloxane and 0.24 parts RHODORSIL PHOTOINIATOR 2074 wasadded. The ink was coated onto PYREX glass plate using a #6 Mayer Bar(nominal wet film thickness was 0.014 mm) and cured as described inExample 22 with a total exposure of 256 W/cm². The coating showed 100percent adhesion measured by ASTM D3359-95a, test Method B. When apermanent marker pen (SHARPIE from Pen & Pencil, Inc. of Bellwood, Ill.)was used to write on the coating, the silicone-containing coating makethe writing beaded up and was easily removed by simple wiping.

EXAMPLE 25

This example shows the use of inks according to the invention to formdurable digital images on ceramic tile. The ceramic tiles used wereglazed ceramic tile 3.5 cm×3.5 cm match gloss black dots (black tiles)match navy dots (blue tiles) obtained from American Olean Tile ofButler, Wis.

Microlith R-A (3 g) was added to 27 g ink vehicle solution(TEOS/3-methacryloxypropyltrimethoxysilane at 3:1 ratio), and milledwith ceramic media (0.3 mm in diameter) on rollers at 25 rpm for 4hours. Rhodorsil photoinitiator 2074 (0.3 g) was dissolved into the ink.Optionally, the catalyst could be dissolved in cyclohexanone at 50percent and then added to the ink.

The ink was printed with an inkjet testbed using MIT printhead at 5000Hz, 35 V. EFOS Ultracure 100SS unit was turned on during the time ofprinting. Characters were printed onto the glazed ceramic tiles.

Firing

The printed samples were heated from 21° C. to 400 ° C. at a heatingrate of 5° C./min, then 400° C. to 1000° C. at heating rate 2.5° C./minusing a heating oven THERMOLYNE (by Sybron). The temperature was held at1000° C. for 5 minutes. The samples were allowed to cool naturally toroom temperature. The fired samples maintained printed pattern andcolor. They showed excellent adhesion to ceramic tile, good abrasionresistance, and solvent resistance.

EXAMPLE 26

This example shows the use of clear-coat protected inks according to theinvention to form durable digital images on ceramic tile. The ink fromthe previous example was printed and cured as before (no firing step)with the same inkjet testbed on retroreflective 3870 High Intensitysheeting, available from 3M Company. The cured printed sample wassprayed with the clear solution. The sample was held at approximately a10 cm distance from the sprayer. (PREVAL SPRAYER from Precision ValveCorp. of Yonkers, N.Y.). The sprayed sample was cured using a FusionSystems UV PROCESSOR fitted with an H-bulb (1.175 w/cm² light intensity)and having a line speed of 50 ft/min (15.2 m/min).

What is claimed is:
 1. A process of forming an imaged article comprisingthe steps of inkjet printing a curable ink composition comprising ahomogeneous mixture of: at least one of: (a) a compound having 2reactive silyl groups, and (b) a compound having at least 3 reactivesilyl groups; an acid generating catalyst; and pigment or pigment chiponto a substrate.
 2. A process according to claim 1 further comprisingthe step of exposing the printed ink composition to actinic radiation inthe presence of moisture to cure the ink composition.
 3. A processaccording to claim 2 further comprising the step of heating thesubstrate and converting the cured ink into a ceramic material.
 4. Aprocess according to claim 2 wherein the cured ink composition comprisesfrom about 10 to about 90 weight percent of at least one compound having2 reactive silyl groups, from about 5 to about 40 weight percent of atleast one compound having at least 3 reactive silyl groups, from about0.1 to about 20 percent by weight of at least one acid generatingcatalyst, and from about 0.1 to about 80 percent by weight of at leastone pigment, based on a total weight of the cured ink composition.
 5. Aprocess according to claim 2 wherein the cured ink composition comprisesfrom about 30 to about 50 weight percent of at least one compound having2 reactive silyl groups, from about 15 to about 25 weight percent of atleast one compound having at least 3 reactive silyl groups, from about0.5 to about 5 weight percent of at least one acid generating catalyst,and from about 2 to about 15 weight percent of at least one pigment,based on a total weight of the cured ink composition.
 6. A processaccording to claim 2 wherein the cured ink composition comprises from 0to about 10 weight percent of at least one compound having 2 reactivesilyl groups, from about 40 to about 95 weight percent of at least onecompound having at least 3 reactive silyl groups, from about 0.1 toabout 20 weight percent of at least one acid generating catalyst, andfrom about 0.2 to about 80 weight percent of at least one pigment, basedon a total weight of the cured ink composition.
 7. A process accordingto claim 2 wherein the cured ink composition comprises from about 2 toabout 5 weight percent of at least one compound having 2 reactive silylgroups, from about 50 to about 80 weight percent of at least onecompound having at least three reactive silyl groups, from about 0.5 toabout 5 weight percent of at least one acid generating catalyst, andfrom about 2 to about 15 weight percent of at least one pigment, basedon a total weight of the cured ink composition.
 8. A process accordingto claim 1 wherein the curable ink composition comprises a homogeneousmixture of: at least one of a hydroxy-terminated polydimethylsiloxane, ahydroxy-terminated polydiethylsiloxane,1,3-dimethyltetramethoxydisiloxane, methacryloxypropyltrimethoxysilane,tetraethoxysilane, 1,3-dioctyltetramethoxydisiloxane,glycidoxy-propyltrimethoxysilane, 3-bromopropyltrimethoxysilane anddioctyltetraetoxydisiloxane; and an acid generating catalyst comprisingan onium salt.
 9. A process according to claim 1 wherein the acidgenerating catalyst comprises an onium salt having a structure L _(W) —Y^(+MX) ⁻ wherein L is an aryl or substituted aryl group; w is an integerfrom 2 to 4; Y is sulfur or iodine; M is a Group III, IV, or V elementfrom the Periodic Table of the Elements; and X is a sulfate, tosylate,alkylsulfonate, fluoroalkylsulfonate, fluoroalkyl, or a perfluorinatedaryl group.
 10. A process according to claim 1 further comprising thestep of inkjet printing a clear coat onto the imaged article, whereinthe clear coat comprises a homogeneous mixture of: at least one of: (a)a compound having 2 reactive silyl groups, and (b) a compound having atleast 3 reactive silyl groups; and an acid generating catalyst.
 11. Aprocess according to claim 1 wherein the pigment has a pigment particlesize ranging from about 10 to about 400 nm.
 12. A process according toclaim 1 wherein the reactive silyl groups are the only acid curablegroups in the ink composition.
 13. A process according to claim 1wherein the ink composition comprises a compound having 2 reactive silylgroups selected from the group consisting of hydroxy-terminatedpolydimethylsiloxanes, hydroxy-terminated polydiethylsiloxanes, andcombinations thereof.
 14. A process according to claim 1 wherein the inkcomposition comprises a pigment selected from the group consisting ofcarbon black, zinc oxide, titanium dioxide, phthalocyanine,anthraquinones, perylenes, carbazoles, monoazobenzimidazolones,disazobenzimidazolones, rhodamines, indigoids, quinacridones,diazopyranthrones, dinitranilines, pyrazolones, diazopyranthrones,dinitranilines, pyrazolones, dianisidines, pyranthrones,tetracholoroisoindolinones, dioxazines, monoazoacrylides,anthrapyrimidines, and combinations thereof.
 15. A process according toclaim 14 wherein the pigment is titanium dioxide.
 16. A processaccording to claim 1 wherein the ink composition comprises pigment chipselected from the group consisting of titanium dioxide/ethyl celluloseresin, carbon black/ethyl cellulose resin, and combinations thereof. 17.A process of forming an imaged article comprising the steps of printinga curable composition comprising a homogeneous mixture of: at least oneof: (a) a compound having 2 reactive silyl groups, and (b) a compoundhaving at least 3 reactive silyl groups; an acid generating catalyst;and pigment or pigment chip onto a substrate; and firing the compositionto convert the composition to a ceramic material.
 18. A processaccording to claim 17 wherein the step of printing comprises inkjetprinting, screen printing, flexographic printing or offset printing. 19.A process according to claim 17 wherein the acid generating catalystcomprises an onium salt.
 20. A process according to claim 19 wherein theonium salt has a structure L _(W) —Y ^(+MX) ⁻ wherein L is an aryl orsubstituted aryl group; w is an integer from 2 to 4; Y is sulfur oriodine; M is a Group III, IV, or V element from the Periodic Table ofthe Elements; and X is a sulfate, tosylate, alkylsulfonate,fluoroalkylsulfonate, fluoroalkyl, or a perfluorinated aryl group.
 21. Aprocess according to claim 17 wherein the step of printing comprises aninkjet printing step.
 22. A process according to claim 17 wherein theink composition comprises a compound having 2 reactive silyl groupsselected from the group consisting of hydroxy-terminatedpolydimethylsiloxanes, hydroxy-terminated polydiethylsiloxanes, andcombinations thereof.
 23. A process according to claim 17 wherein theink composition comprises a compound having 3 reactive silyl groupsselected from the group consisting ofhydroxy-1,3-dimethyltetramethoxydisiloxane,methacryloxypropyltrimethoxysilane, tetraethoxysilane,1,3-dioctyltetramethoxydisiloxane, glycidoxy-propyltrimethoxysilane3-bromopropyltrimethoxysilane, dioctyltetraethoxydisiloxane, andcombinations thereof.
 24. A process according to claim 17 wherein theink composition comprises a pigment selected from the group consistingof carbon black, zinc oxide, titanium dioxide, phthalocyanine,anthraquinones, perylenes, carbazoles, monoazobenzimidazolones,disazobenzimidazolones, rhodamines, indigoids, quinacridones,diazopyranthrones, dinitranilines, pyrazolones, diazopyranthrones,dinitranilines, pyrazolones, dianisidines, pyranthrones,tetracholoroisoindolinones, dioxazines, monoazoacrylides,anthrapyrimidines, and combinations thereof.
 25. A process according toclaim 24 wherein the pigment is titanium dioxide.
 26. A processaccording to claim 17 wherein the ink composition comprises pigment chipselected from the group consisting of titanium dioxide/ethyl celluloseresin, carbon black/ethyl cellulose resin, and combinations thereof. 27.A process of forming an imaged article comprising the steps of: a.inkjet printing a curable ink composition comprising a homogeneousmixture of: at least one of: (a) a compound having 2 reactive silylgroups, and (b) a compound having at least 3 reactive silyl groups; anacid generating catalyst; and pigment or pigment chip onto a substrate,b. curing the ink; and c. overprinting the imaged portion with a clearcoat comprising a homogeneous mixture of: at least one of: (a) acompound having 2 reactive silyl groups, and (b) a compound having atleast 3 reactive silyl groups; and an acid generating catalyst.
 28. Aprocess of forming an imaged article comprising the step of inkjetprinting a clear coat comprising a homogeneous mixture of: at least oneof: (a) a compound having 2 reactive silyl groups, and (b) a compoundhaving at least 3 reactive silyl groups; and an acid generatingcatalyst.
 29. A process according to claim 28 wherein the acidgenerating catalyst comprises an onium salt.
 30. A process according toclaim 28, wherein the clear coat comprises a compound having 2 reactivesilyl groups selected from the group consisting of hydroxy-terminatedpolydimethylsiloxanes, hydroxy-terminated polydiethylsiloxanes, andcombinations thereof.
 31. A process according to claim 28 wherein theclear coat comprises a compound having 3 reactive silyl groups selectedfrom the group consisting of hydroxy-1,3-dimethyltetramethoxydisiloxane,methacryloxypropyltrimethoxysilane, tetraethoxysilane,1,3-dioctyltetramethoxydisiloxane, glycidoxy-propyltrimethoxysilane,3-bromopropyltnmethoxysilane, dioctyltetraethoxydisiloxane, andcombinations thereof.
 32. A process of forming an imaged articlecomprising the steps of inkjet printing a curable ink compositioncomprising a homogeneous mixture of: at least one of: (a) a compoundhaving 2 reactive silyl groups, and (b) a compound having at least 3reactive silyl groups; an acid generating catalyst, wherein the acidgenerating catalyst comprises di(dodecylphenyl)iodoniumhexafluoroantimonate; and pigment or pigment chip onto a substrate. 33.A process according to claim 32 wherein the curable ink compositionfurther comprises 2-isopropylthioxanthone.